If you incremented by n seconds, then as long as n >= 60, increment by minutes instead and subtract 60 from n. When 0 <= n < 60, add that to the current number of seconds. If the result is >= 60, subtract 60 and increment minutes again.

Ditto for minutes & hours.

For hours, just subtract 24 from n until 0 <= n < 24, and then add that to hours. If the result >= 24, subtract 24.

There are more efficient ways to do this involving integer division and modulus operators, but loops are easy and none of this is going to be expensive.